FD: How DENS conquered the construction site with formic acid

The year 2023 was one of milestones for DENS. The start-up's clean generators and batteries can now be found on many a construction site. Symbolic was DENS' move into the large building that solar car builder Lightyear left behind. Top executive Max Aerts (32) looks back on the bumpy road to success.

Exactly one year ago it was. In that first week of January 2023, Dens moved into a huge white tent on the Automotive Campus in Helmond. Techies from the start-up were tinkering together batteries and generators that run on hydrozine, also known as formic acid, a sustainable alternative to diesel. 'Not ideal such a tent, but workable,' looks back at the start-up's young ceo, Max Aerts (32). 'We had to do something anyway. So put in some heaters, put on warm sweaters and go.'
It was an emergency move. Thanks to the nitrogen crisis, Dens had embarked on a growth spurt. All at once there was a demand for excavators, crane trucks and other heavy equipment that did not emit pollutants. Especially after the cancellation of the construction exemption for nitrogen emissions at the end of 2022. Since then, construction has only been allowed if it is certain that vulnerable natural areas will not suffer damage.

'The nitrogen crisis has caused enormous misery, of course, but it has given us a boost'

says Aerts. Until then, hardly anything was happening on sustainability in construction. Now something that used to be only desirable was suddenly a necessity. In many large projects it is: build emission-free or don't build.'And Dens offers solutions for exactly that problem, with clean generators and batteries that can provide large machines with electricity in places where there is no electricity.Only: where were they going to assemble all those batteries and generators? At 800 m2, their former premises were far too small. Aerts: 'We wanted to build a new location on campus, but ran into the full electricity grid.' The start-up couldn't get a large power connection elsewhere in the area either. 'We were really stuck.' So the company ended up in a tent in the middle of winter.


And then Lightyear went bankrupt in late January. Holland's pet company had to lay off 600 employees and cease production of their solar cars while feverishly searching for new investors with deep pockets. In April, Lightyear managed to continue in a very slimmed-down form, but they no longer needed that beautiful, spacious production location, about 100 meters from DENS.Thus, the implosion of one green start-up turned out to be a blessing for another. Dens was able to move into Lightyear's building in mid-May. The only thing now reminiscent of the hip car builder is a partition wall between the production hall and the canteen showing the solar car. 'A little reminder of what can go wrong,' says Aerts as he gives a tour of the production area.Instead of futuristic cars, aggregates are now being keyed together here. From the outside, they look like an average shipping container, but it soon becomes clear how much technology is inside those white boxes. The tour takes you past some sort of super-sophisticated meter boxes and other electrical engineering marvels under construction. In the lab where Dens does chemistry research, glass flasks stand in test stands with countless cords and wires.

The best-kept secret

Aerts points to a flask with a black substance in it reminiscent of cola. 'This is the blacksmith's secret' The black stuff is the catalyst. 'If you inject formic acid into this, it is converted into green hydrogen, which is then converted back into electricity in our generators in a fuel cell. This in turn allows heavy machinery to run on it,' explains Aerts. It is this technique that makes Dens unique.

The process Aerts describes does involve a lot of energy being lost. Nor is it cheap. 'If you just have a good power connection on the building site you don't choose our solution either. It is too expensive. If the construction site is very close to a charging point where the large electric machines can charge, no. Then you can drive back and forth with big batteries. But that is often not the case. Then parties come to us.'

Those parties are large builders such as Heijmans. Dens' systems were used last year in the renovation of the Lower House of Parliament, but were also, for example, at the festival of sailing event The Ocean Race in Denmark. Staff numbers went from 50 to 94, turnover increased tenfold, and the company posted a positive operating result for the first time in the third quarter. 'It really was a year of milestones,' says Aerts.

Naïve dreamer

What started as a student project in 2015 is now a full-fledged company. And actually no longer a start-up either, but rather a scale-up. That road was not easy, Aerts looks back. 'We often bumped our noses.'
In 2018, a student team from Eindhoven University of Technology had developed the technology to the point where they were faced with a choice: stop or go commercial. Aerts had not gotten around to studying for three years, so for him the choice was quickly made. Together with partner Tijn Swinkels, he founded DENS.

'What worked in the lab, we then had to test on a scale 50,000 times larger. Then it turns out that there are things in the literature that work very differently in practice. That's a phase you have to go through. You fall on your face and get back on your feet. It's a good thing I'm a naive dreamer. That's why I never for a moment thought about quitting.'

Not even when things were really bad. Like in 2021 when they had to deliver to four paying customers for the first time. 'Just before the delivery date we found out that a component of the core technology had a lifespan of only a few hundred hours. Way too short. It was a tragedy.' They got a year's postponement.And then something turned out technically wrong again. Aerts can laugh about it now, not at all then. 'It could have been the end of our company. It's still new technology, it doesn't go right all at once.' Fortunately, this time only a few minor adjustments were necessary. By 2022, the first working aggregate was in the field. 'A euphoric moment.'

Financial hardships

Especially since the company had also hung by a thread financially on several occasions. The first round of financing had gone smoothly.

They had generated quite a stir as a student team, bringing Rabobank and the Brabant Development Company, among others, on board. In early 2020, Aerts and Swinkels were about to sign off on a new round of capital when the corona pandemic broke out. Investors put on the brakes. 'We had been working on that deal for almost a year and suddenly everything was in doubt.'

The financers wanted to see contingency plans. And then more plans. It was a time of sleepless nights. They were almost out of money. 'We were now also responsible for employees with families. That then constantly haunts your head. And you want to realize your dream, it's not a hobby project!

At one point Aerts said to the investors: we can make as many plans as you want, but in a month it won't make sense anymore. Then we'll have to fire everyone.' The message got through and the deal came together in the nick of time. Barely recovered from the stress, the next round of financing was already needed. This time Kees Koolen wanted in, made rich with Booking.com and now a major investor in green technology with Koolen Industries. Aerts and his partner wanted him on board. That would give peace of mind and stability. But an investor who was going to exit balked. 'This party wanted one and a half times the deposit back. Much more than had been agreed.

Again, a financing deal threatened to collapse at the last minute. Again, Aerts barely had a month's worth of cash left in the bank. In desperation, he and Swinkels decided to pay the money out of their own pockets. 'Money we had yet to earn. We hadn't paid ourselves a penny that year. It meant we wouldn't get a salary for another year. He shrugged. 'If you want to achieve something, you have to take that pain.' How did they support themselves? 'We were very lucky with our parents. And you can live quite well on €1000 a month if you're on the case 24/7 anyway.

How we are doing now? 'I try not to always come to the business on Sundays anymore.'

Read this article on the website fd.nl

Text: Eva Rooijers

Photography: Rene van der Hulst

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